Anti-skid brake system for an automotive vehicle including brake force control

Abstract

An assumed vehicle body speed is determined on the basis of the wheel speed detected by a wheel speed sensor for each wheel and a slip value indicating the tendency of locking the wheel is determined for a predetermined wheel speed on the basis of the assumed vehicle body speed and a wheel speed of the predetermined wheel. The braking force is controlled on the basis of the slip value. When no braking force is controlled and when at least one of the wheel speeds for all the wheels detected by the wheel speed sensors is larger than the assumed vehicle body speed previously determined, a new assumed vehicle body speed which follows is inhibited from being renewed to a larger value and the new assumed vehicle body speed is set as a value equal to the previous assumed vehicle body speed.

What is claimed is: 
     
       1. An anti-skid brake system for an automotive vehicle, comprising: wheel speed detecting means for detecting a wheel speed of each wheel independently;   assumed vehicle body speed determining means for determining assumed vehicle body speeds based on the wheel speed of each wheel detected by the wheel speed detecting means;   slip value determining means for determining a slip value of a predetermined wheel on the basis of the wheel speed of the predetermined wheel detected by the wheel speed detecting means and the assumed vehicle body speed determined by the assumed vehicle body speed determining means; and   braking force controlling means which controls braking force by increasing, holding and decreasing brake pressure during an ABS control cycle for the predetermined wheel so as not to lock the predetermined wheel at the moment of braking on the basis of the slip value determined by the slip value determining means, wherein prior to the ABS control cycle being performed by the braking force controlling means and when the wheel speed of each wheel detected by the wheel speed detecting means is equal to or smaller than a previous assumed vehicle body speed determined by the assumed vehicle body speed determining means, a next assumed vehicle body speed is maintained as the previous assumed vehicle body speed.   
     
     
       2. An anti-skid brake system as claimed in claim 1, wherein the assumed vehicle body speed determining means maintains the next assumed vehicle body speed as the previous assumed vehicle body speed prior to the ABS control cycle being performed by the braking force controlling means and when the wheel speed of each wheel detected by the wheel speed detecting means is equal to or smaller than the previous assumed vehicle body speed determined by the assumed vehicle body speed determining means, thereby preventing the next assumed vehicle body speed from becoming larger than the previous assumed vehicle body speed. 
     
     
       3. An anti-skid brake system as claimed in claim 2, wherein the assumed vehicle body speed determining means determines the next assumed vehicle body speed by adding a predetermined value to the previous assumed vehicle body speed prior to the ABS control cycle being performed by the braking force controlling means and when the wheel speed of each wheel detected by the wheel speed detecting means is larger than the previous assumed vehicle body speed determined by the assumed vehicle body speed determining means. 
     
     
       4. An anti-skid brake system as claimed in claim 2, wherein the next assumed vehicle body speed is maintained as the previous assumed vehicle body speed, when a maximum wheel speed detected by the wheel speed detecting means is larger than the previous assumed vehicle body speed determined by the assumed vehicle body speed determining means. 
     
     
       5. An anti-skid brake system as claimed in claim 1, wherein the braking force controlling means performs control for reducing, increasing and retaining the braking force. 
     
     
       6. An anti-skid brake system as claimed in claim 5, wherein the braking force controlling means performs the control for at least one of retaining the braking force after the control for reducing the braking force and after the control for increasing the braking force. 
     
     
       7. An anti-skid brake system as claimed in claim 6, wherein the next assumed vehicle body speed is adjustable at a smaller rate during operation of the braking force controlling means when a total period of time required for retaining the braking force in a control cycle is equal to or longer than a predetermined period of time. 
     
     
       8. An anti-skid brake system as claimed in claim 6, wherein the next assumed vehicle body speed is changed at a smaller rate during operation of the braking force controlling means when a total period of time required for reducing the braking force in a control cycle is longer than a predetermined period of time. 
     
     
       9. An anti-skid brake system as claimed in claim 5, wherein the braking force controlling means performs the control for retaining the braking force at the moment of starting the control. 
     
     
       10. An anti-skid brake system as claimed in claim 9, wherein the braking force controlling means starts the control at the moment when the predetermined wheel reaches a predetermined magnitude of deceleration. 
     
     
       11. An anti-skid brake system as claimed in claim 5, wherein the braking force controlling means performs the control for reducing the braking force when the slip value of the predetermined wheel exceeds a predetermined threshold value in a direction in which a tendency of locking the wheel increases. 
     
     
       12. An anti-skid brake system as claimed in claim 5, wherein the braking force controlling means performs the control for increasing the braking force when the slip value of the predetermined wheel exceeds a predetermined threshold value in a direction in which a tendency of locking the wheel decreases. 
     
     
       13. An anti-skid brake system as claimed in claim 5, wherein the next assumed vehicle body speed is changed at a smaller rate during operation of the braking force controlling means when a period of time required for retaining the braking force after a decrease in the braking force is equal to or longer than a predetermined period of time. 
     
     
       14. An anti-skid brake system as claimed in claim 1, wherein: the assumed vehicle body speed determining means comprises first assumed vehicle body speed determining means and second assumed vehicle body speed determining means;   wherein the first assumed vehicle body speed determining means determines a maximum wheel speed detected by the wheel speed detecting means as the next assumed vehicle body speed when the maximum wheel speed exceeds the previous vehicle body speed; and   wherein, when the maximum wheel speed to be detected by the wheel speed detecting means during the control by the braking force controlling means exceeds the previous vehicle body speed by a predetermined value, the second assumed vehicle body speed determining means determines a value obtained by adding a predetermined renewal value to the previous vehicle body speed.   
     
     
       15. An anti-skid brake system as claimed in claim 14, wherein the first assumed vehicle body speed determining means determines the maximum wheel speed as the next assumed vehicle body speed when the maximum wheel speed is larger than the previous assumed vehicle body speed less a further predetermined value. 
     
     
       16. An anti-skid brake system as claimed in claim 14, wherein the first assumed vehicle body speed determining means determines the maximum wheel speed as the next assumed vehicle body speed when the previous assumed vehicle body speed is smaller than a predetermined value.